Alternator D+ advice sought, please!

[Loafer]

Right men, listen in.

 

Is it OK to allow a temporary application of 12V (from battery bank via a switch) to the D+ terminal on an alternator, usually while the engine is NOT running, but also when it IS running (in case I forget to switch it off!).

 

The reason for this is to allow me to tie my two battery banks together on demand, while using a charging source other than my alternator.

 

Thoughts, anyone?

 

 

[nicknorman]

Right men, listen in.

 

Is it OK to allow a temporary application of 12V (from battery bank via a switch) to the D+ terminal on an alternator, usually while the engine is NOT running, but also when it IS running (in case I forget to switch it off!).

 

The reason for this is to allow me to tie my two battery banks together on demand, while using a charging source other than my alternator.

 

Thoughts, anyone?

 

1/ With the engine not running, you'll be putting max current into the alternator's field coil (stator), several amps, so if you forget to turn it off...

 

2/ Normally one does this via a bulb, not sure how wise it would be to give it a hard +12v but of course you could always insert a bulb or resistor to mimic the same conditions as you get with the ignition on.

 

How about a diode between the d+ and relay, with you new connection between the diode and the relay. That way it would only switch on the relay and not affect the alternator. You would lose a little bit of oomph when the alternator drove the relay but I doubt it would be significant.

Edited January 28, 2016 by nicknorman

[Loafer]

1/ With the engine not running, you'll be putting max current into the alternator's field coil (stator), several amps, so if you forget to turn it off...

 

2/ Normally one does this via a bulb, not sure how wise it would be to give it a hard +12v but of course you could always insert a bulb or resistor to mimic the same conditions as you get with the ignition on.

 

How about a diode between the d+ and relay, with you new connection between the diode and the relay. That way it would only switch on the relay and not affect the alternator. You would lose a little bit of oomph when the alternator drove the relay but I doubt it would be significant.

 

Yes, I was thinking a diode might be required. Sounds like the best option.

 

Can you point me to such a diode?

 

Thanks Nick.

[Tony Brooks]

Why mess about with the charging circuit when a switch in a piece of cable between the two bank pos. will do the same - that is unless you have a split charge relay involved. But even they I would feed the relay coil directly. The coil will limit the rotor current (about 3 to 4 amps if fed directly).

 

If one bank is the engine battery I would question the need for charging because unless there is a fault it spends most of the time more or less fully charged. For the odd charge during the winter a simple jump lead will suffice.

[nicknorman]

Yes, I was thinking a diode might be required. Sounds like the best option.

 

Can you point me to such a diode?

 

Thanks Nick.

Which relay is it (need to know coil resistance to know the current)?

[Loafer]

Which relay is it (need to know coil resistance to know the current)?

 

I dunno at the mo, but I'll measure the resistance of it later, if that's any use?

 

 

 

 

 

 

Why mess about with the charging circuit when a switch in a piece of cable between the two bank pos. will do the same - that is unless you have a split charge relay involved. But even they I would feed the relay coil directly. The coil will limit the rotor current (about 3 to 4 amps if fed directly).

 

If one bank is the engine battery I would question the need for charging because unless there is a fault it spends most of the time more or less fully charged. For the odd charge during the winter a simple jump lead will suffice.

 

Thanks Tony

 

Yes, there is a relay involved, I'm just looking for a simple way of operating it manually, for example when I want to give the starter battery a bit of desulphation, which my alternators can't do.

 

I'm not quite with you with the relay current limiting the rotor current. If I add another 12V positive to the relay positive, that will provide the same voltage to D+ but NOT via the relay coil, innit? Therefore, apart from it drawing 4A from my batteries if I leave it on, is that a problem in itself?

[nicknorman]

I'd suggest this diode, at 6A rating it will surely be man enough, probably over-rated but only twice the price of a 1A one that might be marginal. Anyway it's only a quid.

 

http://www.maplin.co.uk/p/p600a-6a-silicon-rectifier-uk59p

[Loafer]

Which relay is it (need to know coil resistance to know the current)?

 

The relay coil is 33 Ohms, Nick.

[dmr]

I am totally confused by this thread.

You talk of joining two banks and also equalising from an external source?

Do you really mean the B+ terminal...the big bugger with the big fat red wire ? (note use of highly technical terms here).

Its fine to join the B+ terminals together, or to apply a higher charging voltage.

The D+ is the ignition light terminal?, I am not even sure that its still called D+, but messing with this won't join the alternators and won't raise the charge voltage, its the feed to the rotor and regulator, so even if you give it a higher voltage the regulator will still control the current so as to maintain the B+ voltage ??????????????/

 

...............Dave

[nicknorman]

The relay coil is 33 Ohms, Nick.

So about 1/2 amp at equalising voltages. 1A diode would probably be enough, but hot engine bay, continuous operation, might as well go for a 3A one as the same price (1/2 quid) http://www.maplin.co.uk/p/1n5402-3a-silicon-rectifier-ql83e

[peterboat]

my starter battery is now 9 years old and has been ignored and abused for all that time if it failed tomorrow it would annoy me but be no loss. i dont think i would try anything with it as it might fall to pieces

[Tony Brooks]

 

I dunno at the mo, but I'll measure the resistance of it later, if that's any use?

 

 

 

 

 

 

 

Thanks Tony

 

Yes, there is a relay involved, I'm just looking for a simple way of operating it manually, for example when I want to give the starter battery a bit of desulphation, which my alternators can't do.

 

I'm not quite with you with the relay current limiting the rotor current. If I add another 12V positive to the relay positive, that will provide the same voltage to D+ but NOT via the relay coil, innit? Therefore, apart from it drawing 4A from my batteries if I leave it on, is that a problem in itself?

 

Perfectly correct - I had a brain fa*t, the bit about the relay coil limiting current is rubbish. As long as the charger is producing more than 4 amps all you need to concern yourself with is the heating effect on the rotor. Personally I do not think it will be a problem but who knows. It will be dissipating around 40 watts and you know how hot a 40 watt bulb gets.

 

I would again question exactly how much good desulphating the starter battery will actually do. The battery spends most of its time all but fully charged so the rate of sulphation will be low. I suspect most fail because the plates have shed materiel and shorted out. Desulphating them might make this worse.

[nicknorman]

I am totally confused by this thread.

You talk of joining two banks and also equalising from an external source?

Do you really mean the B+ terminal...the big bugger with the big fat red wire ? (note use of highly technical terms here).

Its fine to join the B+ terminals together, or to apply a higher charging voltage.

The D+ is the ignition light terminal?, I am not even sure that its still called D+, but messing with this won't join the alternators and won't raise the charge voltage, its the feed to the rotor and regulator, so even if you give it a higher voltage the regulator will still control the current so as to maintain the B+ voltage ??????????????/

 

...............Dave

He already has a spilt charge relay controlled by the D+ , he just wants a means to activate same relay when the alternator isn't spinning (and thus no power on the D+)

[Tony Brooks]

I am totally confused by this thread.

You talk of joining two banks and also equalising from an external source?

Do you really mean the B+ terminal...the big bugger with the big fat red wire ? (note use of highly technical terms here).

Its fine to join the B+ terminals together, or to apply a higher charging voltage.

The D+ is the ignition light terminal?, I am not even sure that its still called D+, but messing with this won't join the alternators and won't raise the charge voltage, its the feed to the rotor and regulator, so even if you give it a higher voltage the regulator will still control the current so as to maintain the B+ voltage ??????????????/

 

...............Dave

 

I think he is looking to pull his split charge relay in so a charger doing an equalisation charge does it to both battery banks. I rather suspect its a bit like "toys for boys" plus another switch to play with.

[WotEver]

Only just got to this thread. Yes, put a diode in the line from D+ to the relay and wire the switch to the relay side of that diode.

 

Then you can't possibly harm the alternator.

 

Tony

[nicknorman]

I rather suspect its a bit like "toys for boys" plus another switch to play with.

Harsh - but then have you seen his gauges?!

 

Anyway a word of caution, if you try to start the engine when the switch is on, you may get lots of current flowing through the relay because after all the domestic battery bank is much bigger than the starter battery. And especially if you operate the switch to start the engine when the start battery is flat for some reason. I foresee lots of smoke and swearing.

Edited January 28, 2016 by nicknorman

[WotEver]

 

I rather suspect its a bit like "toys for boys" plus another switch to play with.

He could wire a pretty light from the switch too, so he wouldn't just have a switch but a lamp too

I foresee lots of smoke and swearing.

And a ready supply of replacement relays...

[Loafer]

 

I think he is looking to pull his split charge relay in so a charger doing an equalisation charge does it to both battery banks. I rather suspect its a bit like "toys for boys" plus another switch to play with.

 

There is some truth in what you say!

 

I just might not bother. I had a spare switch and a suitable place for it.

 

However, it has revealed a good point about the D+ terminal. If I bother, I'll take the diode route. Thanks for the links, Nick.

 

Happy now, thank you everyone.

 

That is all.

[RLWP]

my starter battery is now 9 years old and has been ignored and abused for all that time if it failed tomorrow it would annoy me but be no loss. i dont think i would try anything with it as it might fall to pieces

 

That's because it's mostly only along for the ride. A bit of excitement when it has to start the engine, a big dose of charging on the move then back to sleep again

 

Life is easy for a starter battery.

 

All batteries are consumables and pass away sooner or later

 

Richard

[peterboat]

 

That's because it's mostly only along for the ride. A bit of excitement when it has to start the engine, a big dose of charging on the move then back to sleep again

 

Life is easy for a starter battery.

 

All batteries are consumables and pass away sooner or later

 

Richard

exactly which is why i would not play with it, i do connect mine with jump leads to the main bank so that solar does its stuff on it

[Tony Brooks]

Only just got to this thread. Yes, put a diode in the line from D+ to the relay and wire the switch to the relay side of that diode.

 

Then you can't possibly harm the alternator.

 

Tony

 

Lets look at that to clarify for others (not Nick, Loafer, Wot Ever etc).

 

The split charge relay coil is usually in parallel with the rotor so if you fitted a diode between where ever the feed to the relay is taken off the D+ cable and inserted a diode between that point and the alternator it would indeed prevent another feed to the relay energising the rotor but the same would apply to the warning lamp current so the point it is fitted is critical.

 

It must go into the lead that feeds the relay coil and nothing else. This is likely to be taken form either the warning lamp alternator side terminal or the alternator's D+ terminal. It must not go in the lead between warning lamp and D+ terminal.

[Sir Nibble]

Changeover switch. Common side to relay, changeover terminals to D+ and B+. FUSED!

[WotEver]

Changeover switch. Common side to relay, changeover terminals to D+ and B+. FUSED!

Snib, that's neat ?

 

Tony

[Loafer]

Changeover switch. Common side to relay, changeover terminals to D+ and B+. FUSED!

 

I wondered if you might chip in, Snibs!

 

I presume your idea is to put the fuse between the relay common and the changeover switch common terminal? So that the relay coil is fuse protected in either switch position?

 

(I am slightly slower on the uptake than either of Wotever and Nicknorman!) ETA: And Tony B!

Edited January 28, 2016 by Loafer

[Loafer]

 

Lets look at that to clarify for others (not Nick, Loafer, Wot Ever etc).

 

The split charge relay coil is usually in parallel with the rotor so if you fitted a diode between where ever the feed to the relay is taken off the D+ cable and inserted a diode between that point and the alternator it would indeed prevent another feed to the relay energising the rotor but the same would apply to the warning lamp current so the point it is fitted is critical.

 

It must go into the lead that feeds the relay coil and nothing else. This is likely to be taken form either the warning lamp alternator side terminal or the alternator's D+ terminal. It must not go in the lead between warning lamp and D+ terminal.

 

Tony, thank you for that. I don't have the mental clarity, right now, to think it through from my armchair, but it reads like it's important enough to look at tomorrow. I DO apologise, but I'm suffering from Alcohol-Induced Dickhead Syndrome and it will take it's own time to recover.

 

I've set a reminder on me phone for tomorrow!